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Subject: K 2.6 test6 strange signal behaviour
From: Ken Foskey <foskey@optushome.com.au>
To: linux-kernel@vger.kernel.org
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Date: Mon, 20 Oct 2003 23:01:26 +1000
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I have a problem with signals.

I get multiple signals from a single execution of the program.  I have
attached a stripped source.  Here is the critical snippet, you can see
the signal handler being set before each call:

	signal( SIGSEGV,	SignalHdl );
	signal( SIGBUS,		SignalHdl );
	fprintf( stderr, "Running \n" );
	result = func( eT, p );
	fprintf( stderr, "Finished \n" );
	signal( SIGSEGV,	SIG_DFL );
	signal( SIGBUS,		SIG_DFL );

When I run the code, that does 2 derefs of NULL you will see 2 instances
of "Running" and the handler is not invoked at all for the second time.

./solar:


Getting from NULL
Setting Jump
Running
Signal 11 caught
After jump
Setting to NULL
Setting Jump
Running
Segmentation fault

I am running debian version of K 2.6 test6.  This has occurred on all
versions of K2.6 though, not specific.

-- 
Thanks
KenF
OpenOffice.org developer

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#include <stdio.h>
#include <signal.h>
#include <setjmp.h>

/*************************************************************************
|*	Typdeclarations for memory access test functions
*************************************************************************/
typedef int (*TestFunc)( void* );

/*************************************************************************
*************************************************************************/
static jmp_buf check_env;
static int bSignal;
static void SignalHdl( int sig )
{
  bSignal = 1;
  
  fprintf( stderr, "Signal %d caught\n", sig );
  longjmp( check_env, sig );
}

/*************************************************************************
*************************************************************************/
void check( TestFunc func, void* p )
{
  int result;

  fprintf( stderr, "Setting Jump\n" );
  if ( !setjmp( check_env ) )
  {
	signal( SIGSEGV,	SignalHdl );
	signal( SIGBUS,		SignalHdl );
    fprintf( stderr, "Running \n" );
	result = func( p );
    fprintf( stderr, "Finished \n" );
	signal( SIGSEGV,	SIG_DFL );
	signal( SIGBUS,		SIG_DFL );
  }
  fprintf( stderr, "After jump \n" );
}

/*************************************************************************
*************************************************************************/
static int GetAtAddress( void* p )
{
  return *((char*)p);
}

/*************************************************************************
*************************************************************************/
static int SetAtAddress( void* p )
{
  return *((char*)p)	= 0;
}

/*************************************************************************
*************************************************************************/
void CheckGetAccess( void* p )
{
  check( (TestFunc)GetAtAddress, p );
}
/*************************************************************************
*************************************************************************/
void CheckSetAccess( void* p )
{
  check( (TestFunc)SetAtAddress, p );
}

/*************************************************************************
*************************************************************************/
int main( int argc, char* argv[] )
{
  {
	char* p = NULL;
	fprintf( stderr, "Getting from NULL\n" );
    CheckGetAccess( p );
	fprintf( stderr, "Setting to NULL\n" );
    CheckSetAccess( p );
	fprintf( stderr, "After Setting to NULL\n" );
  }

  exit( 0 );
}

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